Lenticular photography systems typically make use of a lenticular lens sheet which is an array of identical elongate lenticular lenses, or lenticules, usually elongate convex lenses on an upper display surface of the sheet. The sheet normally has a planar lower surface. A lenticular photograph, for example a lenticular representation of a stereoscopic image (eg a three dimensional image or an animation) is formed when a suitably-produced composite interlaced image is printed or secured to the lower surface so as to be viewable through the sheet. The composite comprises elongate strips of images which are appropriately interlaced and dimensioned so as to be aligned with the overlying lenses. The specific characteristics of the lenticular photograph/product are determined by the particular dimensions, shape and design of the convex lenses and the composite interlaced image.
A typical lenticular lens sheet 100, as well known in the art, is shown in a cross sectional view in FIG. 1. The sheet 100 is manufactured from a transparent medium 110 which has a planar lower surface 140 and an upper surface comprising a longitudinal array of elongate protrusions 120 and recesses 130. The elongate protrusions 120 and recesses 130 form lenticular lenses on the upper surface of the sheet.
A lenticular product/photograph includes a composite interlaced image (not shown) located beneath the lenticular lens sheet. The composite interlaced image, comprising elongate strips of images, is suitably aligned with the lenticular lens sheet. Typically, the composite image is printed directly onto the lower planar surface 140 of the transparent medium.
Each strip is viewable through the lenticular lens sheet only at certain viewing angles. The dimensions of the lenticular lenses and the separation distance between the lenticular lens sheet and the composite interlaced image determine the appropriate viewing angle of each strip of the interlaced image.
The elongate strips are suitably dimensioned, aligned with the lenses and interlaced such that the specific elongate strips viewable by the view from a certain viewing angle form an image. The lenticular product is typically designed such that a different image is observed at different viewing angles.
An appropriately-composed interlaced image located under a suitably constructed lenticular lens sheet enables a viewer to perceive various effects such as binocular disparity, whereby each of the viewer's eyes, having different viewing angles to the sheet, sees a different elongate stripe. Binocular disparity is an effect that is used in lenticular products for displaying images which are perceived by a viewer as three dimensional images. Alternatively, the interlaced strips of image and lenticular lens sheet can be arranged so that a viewer, when viewing the sheet from a certain angle, sees the same set of strips from each eye, the viewable strips forming an image. When the viewer views the lens from a different angle, a different set of strips is seen, forming a different perceived image. Thus the image which is perceived by the viewer changes in dependence upon the viewer's viewing angle. Such an effect may be used for displaying short animations.
In order that the desired imaging effect is properly perceived by the viewer, it is necessary for the composite interlaced image to be accurately aligned with the lenticular lens sheet with the elongate image strips parallel to the longitudinally arranged array of elongate protrusions and recess.
Lenticular printing to produce animated or three dimensional effects as a mass-production technique started in the 1940s. The most common method, which accounts for the vast majority of lenticular images in the world today, is lithographic printing directly onto a lenticular lens sheet. However, in order to print directly onto the sheet, it is necessary to register and align the sheet very precisely with the printer.
Accordingly, a significant problem with the manufacture of lenticular products, such as lenticular photographs, is the registration and alignment of the composite interlaced image with respect to the lenticular lens sheet. When the composite interlaced image is to be directly printed onto the lower surface of the lenticular lens sheet, it is necessary to register and align the lenticular lens sheet with respect to the printing head.
There have been a variety of previous attempts to produce registration and alignment systems to register the precise location of the lenticular lenses and to align them with a composite interlaced image. Such systems have been designed to account for inaccuracies inherent in the manufacture of lenticular lens sheets and, in particular, inaccuracies resulting from embossing using an engraved cylinder. Alignment of the lens is especially important where the composite interlaced image is printed directly on to the lenticular lens screen. Misalignment and non-suitable registration leads to ineffectual lenticular products and expensive wastage of materials and production costs.
Most registration devices are complex systems which rely on the optical properties of the lenticular lens sheet itself. Usually such devices employ a light emitter and detector system to measure changes in contrast and focusing properties of the lenticular lens sheet.
The system according to embodiments of the present invention seeks to alleviate the problems associated with the prior art and provide a simple and inexpensive registration and alignment device for lenticular lens sheets.